The present invention relates to a method for the continuous marking of elongated material, such as a wire strand, which is moved in its longitudinal direction, in which method, ring-shaped markings which are limited in axial direction are applied to the surface of the material by means of color jets. The color jets emerge under pressure from at least one oscillating nozzle which is driven by an electrical oscillating system, and impinge at a right angle to the direction of movement of the material onto the surface thereof. A frequency of the oscillation system is controlled to be proportional to a rate of removal of the material at which the material is moved past the nozzle (Federal Republic of Germany Patent 14 65 660).
"Elongated Material" within the meaning of the invention is, for instance, electrical lines, such as, for instance, control lines or else insulated strands of communications cables to which the following description refers by way of example for all other applications. Instead of the words "elongated material" there will accordingly be used the word "strand".
The color marking of strands is required for communications cables so that easy identification of individual strands is possible for installation. Thus, for example, in the case of four strands which are to be twisted to form a so-called "quad", rings are sprayed onto the insulation of three of these strands, each strand being marked differently. The fourth strand remains free. The marking of the three strands can be effected in the manner that the first strand is given single rings, the second strand double rings at short distances apart and the third strand double rings at larger distances apart. The strands can also be provided with markings in different colors.
Federal Republic of Germany Patent 14 65 660 describes a method in which a device is used which has become known by the commercial name "Colomat". By means of this device the markings are sprayed onto the insulation of the strands directly after application of the insulating material to the conductors of the strands. The frequency of the oscillation system and thus also the frequency of the nozzle are controlled as a function of the rate of removal of the strand. For this purpose there is used, for instance, a disk which is carried along by the strand and rotated thereby, and which is coupled to a sine wave generator. The output signal of the sine wave generator is converted into electrical pulses which serve to control the oscillation system. The frequency of the output signal determines the axial distance between the markings on the strand. This frequency is determined by the diameter of the disk. If the distance between the markings is to be changed, then another disk having another diameter must be used. This is not possible in continuous operation.